What exactly is RESTful programming?

Question

What exactly is RESTful programming?

Answer 1

I see a bunch of answers that say putting everything about user 123 at resource "/user/123" is RESTful.

Roy Fielding, who coined the term, says REST APIs must be hypertext-driven. In particular, "A REST API must not define fixed resource names or hierarchies".

So if your "/user/123" path is hardcoded on the client, it's not really RESTful. A good use of HTTP, maybe, maybe not. But not RESTful. It has to come from hypertext.